Fluorocarbon based solvents have been used extensively for the degreasing and otherwise cleaning of solid surfaces, especially intricate parts and difficult to remove soils.
In its simplest form, vapor degreasing or solvent cleaning consists of exposing a room-temperature object to be cleaned to the vapors of a boiling solvent. Vapors condensing on the object provide clean distilled solvent to wash away grease or other contaminants. Final evaporation of solvent from the object leaves the object free of residue. This is contrasted with liquid solvents which leave deposits on the object after rinsing.
A vapor degreaser is used for difficult to remove soils where elevated temperature is necessary to improve the cleaning action of the solvent, or for large volume assembly line operations where the cleaning of metal parts and assemblies must be done efficiently. The conventional operation of a vapor degreaser consists of immersing the part to be cleaned in a sump of boiling solvent which removes the bulk of the soil, thereafter immersing the part in a sump containing freshly distilled solvent near room temperature, and finally exposing the part to solvent vapors over the boiling sump which condense on the cleaned part. In addition, the part can also be sprayed with distilled solvent before final rinsing.
Vapor degreasers suitable in the above-described operations are well known in the art. For example, Sherliker et al., in U.S. Pat. No. 3,085,918 disclose such suitable vapor degreasers comprising a boiling sump, a clean sump, a water separator, and other ancillary equipment.
Cold cleaning is another application where a number of solvents are used. In most cold cleaning applications the soiled part is either immersed in the fluid or wiped with cloths soaked in solvents and allowed to air dry.
Recently, nontoxic, nonflammable fluorocarbon solvents liks trichlorotrifluoroethane have been used extensively in degreasing applications and other solvent cleaning applications. Trichlorotrifluoro-ethane has been found to have satisfactory solvent power for greases, oils, waxes and the like. It has therefore found widespread use for cleaning electric motors, compressors, heavy metal parts, delicate precision metal parts, printed circuit boards, gyroscopes, guidance systems, aerospace and missile hardware, aluminum parts and the like.
The art has looked towards azeotropic compositions having fluorocarbon components because the fluorocarbon components contribute additionally desired characteristics, such as polar functionality, increased solvency power, and stabilizers. Azeotropic compositions are desired because they do not fractionate upon boiling. This behavior is desirable because, in the previously described vapor degreasing equipment with which these solvents are employed, redistilled material is generated for final rinse-cleaning. Thus, the vapor degreasing system acts as a still. Therefore, unless the solvent composition is essentially constant boiling, fractionation will occur and undesirable solvent distribution may act to upset the cleaning and safety of processing. For example, preferential evaporation of the more volatile components of the solvent mixtures, would result in mixtures with changed compositions which may have less desirable properties, such as lower solvency towards soils, less inertness towards metal, plastic or elastomer components, and increased flammability and toxicity.
The art is continually seeking new fluorocarbon-based azeotropic mixtures or azeotrope-like mixtures which offer alternatives for vapor degreasing and other cleaning applications. Currently, fluorocarbon-based azeotrope-like mixtures are of particular interest, because they are considered to be stratospherically safe substitutes for presently used fully halogenated chlorofluorocarbons. The latter have been implicated in causing environmental problems in connection with the depletion of the earth's protective ozone layer. Mathematical models have substantiated that hydrochlorofluorocarbons, like dichlorotrifluoroethane (HCFC-123 or HCFC-123a), have a much lower ozone depletion potential and global warming potential than the fully halogenated species.
Accordingly it is an object of the invention to provide novel environmentally acceptable azeotropic compositions based on dichlorotrifluoroethane which are useful in a variety of industrial cleaning applications.
It is another object of the invention to provide azeotrope-like compositions which are liquid at room temperature and which will not fractionate under conditions of use.
A further object of the invention is to provide azeotrope-like compositions which are nonflammable in both the liquid and vapor phases.
Other objects and advantages of the invention will become apparent from the following description.